1. Field of the Invention
The invention relates to resonant circuits and, in particular, to LC resonant circuits.
2. Description of the Related Art
In circuit design, to accomplish signal transmission, an inductor and a capacitor connected in parallel are often used in an LC resonant circuit, as shown in FIG. 1A. To filter signal, an inductor and a capacitor connected in series are often used in an LC resonant circuit, as shown in FIG. 1B.
An LC resonant circuit is often formed with an independent inductor and an independent capacitor, connected either in series or in parallel, on a substrate. The independent inductor can be a plane inductor, a spiral inductor, or the like and a schematic diagram thereof is shown in FIG. 2. The independent capacitor can be an MIM (metal-insulator-metal) capacitor, a POP (poly-on-poly) capacitor, or the like. The inductor and the capacitor are independent; that means, they do not overlap each other in layout. The substrate can be PCB substrate, LTCC substrate, GaAs substrate, silicon substrate, SOI substrate, or the like. If such LC resonant circuit is formed on an insulating substrate, excellent signal transmission and filtering can be obtained due to electrical insulation of the insulating substrate. However, a substrate in a typical semiconductor process is semi-conductive. As a result, energy of a high frequency signal is lost due to signal loss via the semi-conductive substrate. Accordingly, LC resonant circuit designed by traditional methods cannot result in satisfied signal transmission and filtering.